High frequency circuits for electron tubes and tubes comprising such circuits

ABSTRACT

High frequency circuits for the anodes of electron tubes, in particular magnetrons. There is associated with the usual cavities of said anodes a second high frequency circuit arranged in parallel with the first one constituted by said cavities, to provide coupling between adjacent cavities and to maintain their pi mode operation despite possible geometrical differences. Moreover, by making the second circuit an absorptive one, other unwanted modes are suppressed.

United States Patent [1 91 Chavanat et a1.

[ June 26, 1973 1 HIGH FREQUENCY CIRCUITS FOR ELECTRON TUBES AND TUBES COMPRISING SUCH CIRCUITS [75] Inventors: Paul Chavanat; Bernard Epsztein;

Georges Mourier, all of Paris, France [73] Assignee: Thomson-CS1", Paris, France [22] Filed: Dec. 15, 1971 [21] Appl. No.: 208,157

[30] Foreign Application Priority Data Dec. 22, 1970 France 7046248 7 [52] Cl 315/3951, 315/3963, 315/3965, 331/88 [51] Int. Cl. H01] 25/50 [58] Field of Search 315/3963, 39.65,

[56] References Cited UNITED STATES PATENTS 2,826,719 3/1958 Donal, Jr. 315/3963 3,384,783 5/1968 Olson, Jr 315/3965 X 3,032,681 5/1962 Scanzani 316/3965 X 2,808,568 10/1951 315/39.63 X 2,828,441 3/1958 Jenny 315/3963 X Primary Examiner-Rudolph V. Rolinec Assistant ExaminerSaxfield Chatmon, Jr. Attorney-John W. Malley, G. Lloyd Knight et a1.

[5 7] ABSTRACT High frequency circuits for the anodes of electron tubes, in particular magnetrons.

There is associated with the usual cavities of said anodes a second high frequency circuit arranged in parallel with the first one constituted by said cavities, to provide coupling between adjacent cavities and to maintain their 11' mode operation despite possible geometrical differences. Moreover, by making the second circuit an absorptive one, other unwanted modes are suppressed.

15 Claims, 11 Drawing Figures HIGH FREQUENCY CIRCUITS FOR ELECTRON TUBES AND TUBES COMPRISING SUCH CIRCUITS magnetic coupling between which, in normal operation, is very loose, and the vital tuning of which to the same frequency, necessitates high precision machining with a consequent increase in cost and'reduction in manufacturing efficiency.

Another major drawback resides in the fact that the magnetron anode is liable to resonate at a large number of different frequencies corresponding not only to the useful mode which is the n mode and will be described hereinafter, providing as it does tight coupling with the load, but also to other resonance modes;.th'ese modes are generally very loosely coupled with the load and can consequently result in a high over-voltage; there is thus the risk that they will adversely affect the effective mode and give rise to irregularities in operation which are known as mode jumps.

Finally, magnetron tubes have a third disadvantage also associated with the structure of their high frequency circuit, namely that they produce a limited frequency band which, in certain applications, means that they are abandoned in favor of other more expensive and less efficient tubes which provide a wider range of possibilities as far as output frequency is concerned.

The present invention relates to an improved anode which enables these difficulties to be overcome and which, in principle, involves the association with the conventional main anode high frequency structure, of a second, separate periodic structure coupled to the first either electrically or magnetically or by both means.

According to the present invention there is provided a high frequency circuit for a magnetron tube, comprising two high frequency structures, respectively a main and a secondary one, arranged parallel with one another on a cylindrical wall, each comprising conductor elements which define between them identical spaces within which electromagnetic fields take place, the conductor elements of the secondary structure producing electromagnetic coupling between any two of said adjacent spaces in the main structure when, in operation the conductor elements of said main structure have equal and opposite electrical polarities.

The invention will be better understood from a consideration of the ensuing description and by reference to the attached figures in which:

F108. 1 and 2 illustrate a device in accordance with the invention;

FIGS. 3, 4, 5, 6, 7, 8 and 9 illustrate variant embodiments of the invention;

FIG. 10 illustrates a particular variant embodiment which enables the operating frequency to be altered;

FlG. ll schematically shows an improved magnetron in accordance with the invention.

FIGS. 1 and 2 respectively illustrate in section and in elevation, part of a high frequency structure for a tube in accordance with the invention.

The main structure or high frequency line 8, comprises spaces marked 1, 2 and 3 which form resonant cavities, separated by walls 4, 5, 6, 7 which throughout the remainder of the description will be referred to as fins although they can take more compact forms, similar to bars. The number of such fins, which is equal to the number of cavities thus delimited, determines a space periodicity of the cavities upon the periphery of the main structure, which is called base period.

In accordance with the invention, a second structure or secondary high frequency line, 9, is arranged concentrically to the first in such fashion that its fins, l0, 11, 12, have their axes contained in the plane of symmetry of each of the cavities 1,2,3. The combination of these two structures which appears in the whole embodiments of the invention, provides a space periodicity which is half the base period, each one of said cavities being divided into two parts.

The operation of this kind of system is as follows If we consider the main line 8, the propagation of a microwave results there; for a specific frequency, in the production at the end of the fins 4, 5, 6, of instantaneous voltages of equal and opposite polarities considered from one fin to the next, this corresponding as far as the wave is concerned to a vibrational state which is out of phase by or 1r radians; this kind of propagation is known as 1r mode propagation and constitutes the effective mode for normal operation of the magnetron.

In this mode, if we take for example the lines of force of the corresponding high frequency magnetic field, such as l3, 14, 15 the electromagnetic energy coming from the cavity 1 has a flux which is equal and opposite to that entering the cavity 2 at the same instant Any geometrical asymmetry in the presentcavities will lead to a disturbance of this oscillatory mode since there is no coupling between them which could compensate for these local irregularities.

It is the function of the second structure 9 to eliminate this undesired phenomenon by providing electromagnetic coupling between the cavities. 'Each of its fins, 10,11, 12 is arranged, as already indicated, with its two adjacent ones of said fins, the energy flux leaving the half interspace 20 between fins, is of the same magnitude as the energy flux entering the half interspace 2'1 and the algebraic sum of these fluxes is 0 no energy circulates through the second structure. I

By contrast, if because of some geometric irregularity in the cavities, the 11' mode is disturbed, an imbalance occurs between the output and input fluxes so that the.

result of the algebraic sum of the fluxes at the second structure is no longer 0, giving rise to the appearance of an electric current and the propagation of a certain energy quantity, corresponding to a coupling effect and thus providing the desired interdependence betweenthe cavities of the main structure.

First, the desired 1r mode operation is restablished by the addition to the main high frequency structure of a second structure associated therewith and coupled thereto, the action of which is to correct the influence of the geometric irregularities therein; said second structure facilitates the propagation around the anode, which propagation is critical around the 1r mode.

It should be borne in mind that the coupling of the second structure with the main structure 8 may have a second effect, namely that of slightly altering the 1r mode frequency of the assembly in relation to the or mode frequency of the main structure on its own.

Finally, it has a third effect Near the working point, propagation of electromagnetic energy along each of the two structures takes place in respective opposite directions; in accordance with conventional terminology the dispersion curves of said structures thus have slopes of opposite sign.

FIG. 2 illustrates a first variant embodiment of the invention where a material 22 choosen for providing a maximum absorbing effect is arranged in proximity of the fins of the second structure; the case illustrated on the figure corresponds to the use of a material such as Kanthal (registered trade mark), which is deposited directly upon said fins by the Schoop process.

This embodiment is designed to eliminate the second above-mentioned phenomenon inherent in high frequency magnetron structures, namely the possibility of the incurrence of modes other than the desired 1r mode however, these interference modes, which result in the incurrence of parasitic frequencies in the high frequency output from the tube, do not, unlike the case with the 1r mode, produce a zero resultant electromagnetic energy at the location of each element in the second structure, so that the latter is thus the source of perceptible wave propagation; this difference between the distribution of the fields corresponding respectively to the nmode and to the parisitic modes, offers a possibility of absorbing the latter without at any rate in the former, thus preventing the high frequency circuit from partially operating in accordance with modes other than the ar mode.

The 1r mode operation on its own is thus determined by dissipation of the corresponding parasitic energy, by ohmic losses in the absorbent material which have been applied to the second structure.

Any other material which, by virtue of its constitution or form, has electromagnetic energy absorption characteristics, can of course be used.

FIG. 3 illustrates another variant embodiment where the fins of the second structure are provided with a terminal plate 23 to increase the capacitance and therefore the coupling with the main high frequency structure.

FIG. 4 illustrates another variant embodiment derived from that of FIG. 3 by symmetrical doubling in the latters plane, of the main high frequency structure; the fins of the second structure occupy said medium plane and the need to effect coupling between them leads to the production of an opening such as 24 in the wall of each cavity. The tight coupling between the two structures is then magnetic in nature.

FIG. 5 illustrates a variant embodiment derived from that of FIG. 4 by the discarding of the terminal plates; the coupling between the fins 25 of the second structure is then effected directly through the medium of the electromagnetic fields overlapping into the interaction space. FIGS. 6, 7 and 8 illustrate three other embodiments all derived from that of FIG. 5, differing in resp'ect thereof by the fact that the fins of the second structure coupled with the main high frequency structure have been arranged on the exterior of the cylindrical surface and not inside it the orifices 26 and 27 are required to provide coupling between the two struc- ICUI'CS.

In FIG. 7 the fins are given a length such that they define between one another closed resonant cavities 28 through which coupling is effected and which are normally empty of electromagnetic energy in the correct operating mode.

In FIG. 8 these cavities extend partly into the walls of the cavities of the main structure.

FIG. 9 illustrates a variant embodiment of the invention shown in FIG. 1, where each fin arranged at the edge of the main high frequency structure is provided with a supplementary leg 30 at right angles, these legs penetrating respectively between the walls of each resonant cavity of said structure, this considerably increasing the coupling between the two structures, which coupling in this case is principally electrical in nature.

FIG. 10 illustrates a variant embodiment of the device shown in FIG. 9 where the penetration of the additional rightangled leg is made variable by the provision of a mechanical device for producing relative displacement between the two structures (said device not having been shown). The result of this kind of displacement is a variation in the frequency of the high frequency 1r mode wave.

The variation of the mode frequency and optimum coupling between the two structures in order to main tain the mode, both depend upon electrical quantities associatedwith the interpenetration of the movable leg of the fin. In order to simultaneously satisfy these two conditions, said leg has a profile 31 whose curvature has been determined theoretically or experimentally and is designed, for any interpenetration to maintain optimum coupling throughout the corresponding frequency band.

The combination of a second mobile structure in accordance with the invention, with the high frequency structure of a magnetron, thus enables a variable frequency electron tube to be produced.

FIG. 11 schematically shows in section a magnetron provided with a high frequency structure according to the invention. The structure shown here is that one shown in FIG. 5 any structure of the invention, and particularly that one of FIG. 10, may of course be used for constituting an anode of magnetron.

The high frequency structure 51 is arranged around the cathode 50; coupling devices supplying and extracting high frequency energy are schematically shown by 52 and 53.

What is claimed, is

1. In a multi-cavity magnetron, an anode structure comprising two high frequency structures, respectively a main and a secondary one, arranged parallel with one another on a cylindrical wall, said main structure comprising, disposed onto the said cylindrical wall, a plurality of identical high frequency adjacent cavities separated by conductor elements, and constituting a main high frequency circuit, said secondary structure comprising, disposed onto the said cylindrical wall, conductor elements defining between them identical spaces, and constituting a secondary high frequency circuit said secondary high frequency circuit being disposed relative to said main circuit in such a way that the two circuits are coupled, each space of the secondary circuit producing electromagnetic coupling between two adjacent cavities of the main circuit.

2. An anode structure as claimed in claim 1, in which the conductor elements of said secondary structure are arranged in the plane of symmetry of said cavities which contains the axis of said cylindrical wall, thereby dividing each of said cavities into two identical parts.

3. An anode structure circuit as claimed in claim 1, in which said conductor elements of the two high frequency structures are arranged at the same side of said wall.

4. An anode structure as claimed in claim 1, in which the conductor elements of the two high frequency structures are respectively located at either side of said wall.

5. An anode structure as claimed in claim 1, in which said cavities of the main structure and said identical spaces of the secondary structure are coupled by holes provided within their walls.

6. An anode structure as claimed in claim 1, in which said spaces and cavities have dimensions which are such as to cause them to exhibit electromagnetic resonance at the same frequency.

v 7. An anode structure as claimed in claim 1, in which at least part of the conductor elements of one of the said relative movement is a translatory one in a direction parallel to the axis of said cylinder.

10. An anode structure as claimed in claim 1, in which said identical spaces of said secondary structure extend in part at least into a space created within said conductor elements of the main high frequency structure.

11. An anode structure as claimed in claim 1, in which said conductor elements of the secondary structure take the form of bars located externally of said adjacent cavities on the main structure.

12. An anode structure as claimed in claim 11, in which said bars terminate in a further bar perpendicular to them, and giving them a T-shape, said further bar being parallel to an external edge of the conductor elements of said main structure.

13. An anode structure as claimed in claim 1, in which said conductor elements of the secondary structure take the form of plates located inside said adjacent cavities of the main structure.

14. An anodestructure as claimed in claim 1, in which said conductor elements of the secondary structure takethe form of bars located inside said adjacent spaces of the main structure.

15. An anode structure as claimed in claim 14, in which said elements are terminated in a perpendicular rod or bar producing a T-shape arrangement, said bar being parallel to an external edge of the conductor elements of said main structure, which conductor elements are provided with openings opposite the ends of the perpendicular bars to provide coupling between said bars. 

1. In a multi-cavity magnetron, an anode structure comprising two high frequency structures, respectively a main and a secondary one, arranged parallel with one another on a cylindrical wall, said main structure comprising, disposed onto the said cylindrical wall, a plurality of identical high frequency adjacent cavities separated by conductor elements, and constituting a main high frequency circuit, said secondary structure comprising, disposed onto the said cylindrical wall, conductor elements defining between them identical spaces, and constituting a secondary high frequency circuit said secondary high frequency circuit being disposed relative to said main circuit in such a way that the two circuits are coupled, each space of the secondary circuit producing electromagnetic coupling between two adjacent cavities of the main circuit.
 2. An anode structure as claimed in claim 1, in which the conductor elements of said secondary structure are arranged in the plane of symmetry of said cavities which contains the axis of said cylindrical wall, thereby dividing each of said cavities into two identical parts.
 3. An anode structure circuit as claimed in claim 1, in which said conductor elements of the two high frequency structures are arranged at the same side of said wall.
 4. An anode structure as claimed in claim 1, in which the conductor elements of the two high frequency structures are respectively located at either side of said wall.
 5. An anode structure as claimed in claim 1, in which said cavities of the main structure and said identical spaces of the secondary structure are coupled by holes provided within their walls.
 6. An anode structure as claimed in claim 1, in which said spaces and cavities have dimensions which are such as to cause them to exhibit electromagnetic resonance at the same frequency.
 7. An anode structure as claimed in claim 1, in which at least part of the conductoR elements of one of the two structures at least, is equipped with a material absorbent for electromagnetic waves.
 8. An anode structure as claimed in claim 1, in which the conductor elements of said main and secondary structures are movable in relation to one another.
 9. An anode structure as claimed in claim 8, in which said relative movement is a translatory one in a direction parallel to the axis of said cylinder.
 10. An anode structure as claimed in claim 1, in which said identical spaces of said secondary structure extend in part at least into a space created within said conductor elements of the main high frequency structure.
 11. An anode structure as claimed in claim 1, in which said conductor elements of the secondary structure take the form of bars located externally of said adjacent cavities on the main structure.
 12. An anode structure as claimed in claim 11, in which said bars terminate in a further bar perpendicular to them, and giving them a T-shape, said further bar being parallel to an external edge of the conductor elements of said main structure.
 13. An anode structure as claimed in claim 1, in which said conductor elements of the secondary structure take the form of plates located inside said adjacent cavities of the main structure.
 14. An anode structure as claimed in claim 1, in which said conductor elements of the secondary structure take the form of bars located inside said adjacent spaces of the main structure.
 15. An anode structure as claimed in claim 14, in which said elements are terminated in a perpendicular rod or bar producing a T-shape arrangement, said bar being parallel to an external edge of the conductor elements of said main structure, which conductor elements are provided with openings opposite the ends of the perpendicular bars to provide coupling between said bars. 